Biomolecular nanoparticles are increasingly prevalent as diagnostic tools, molecular delivery carriers, and models for engineered nanocompartments. To better understand their molecular and structural characteristics, it is particularly useful to extract as much information as possible from single individuals in solution-phase conditions. However, detailed observation of a single nanoparticle is limited by the short observation times afforded by its Brownian motion. Using interferometric scattering as a highly sensitive label-free detection scheme, we recently developed the Interferometric Scattering Anti-Brownian ELectrokinetic (ISABEL) trap to hold a single nanoparticle in solution for extended optical observation. Here, I describe the working principles of the ISABEL trap, and demonstrate initial experiments studying the carboxysome, a fascinating carbon fixation microcompartment found in autotrophic bacteria. By moving scattering detection to the near infrared, we leave the UV-visible spectral region open for fluorescent protein spectroscopic biosensors to study, for example, the redox chemistry inside single carboxysomes. These experiments benefit from rich correlative measurements utilizing both scattering and fluorescence, with many exciting future capabilities within reach.
The nucleosome is a hub of genetic processes and is thus the target of gene regulatory enzymes and factors. My laboratory is interested in understanding how chromatin enzymes and factors interact with their nucleosome substrates to achieve the appropriate biological outcome. I will discuss principles for how the nucleosome is recognized by chromatin enzymes and factors gleaned from the collective structural and biochemical studies from my and other laboratories.
Last update: 4/4/2025, Ralf Bundschuh